/**
 * CHitQueue.java
 *
 * Copyright 2007 easou, Inc. All Rights Reserved.
 *
 * created by jay 2010-6-18
 */
package org.apache.lucene.search;

import org.apache.lucene.util.PriorityQueue;

final class CHitQueue extends PriorityQueue<CFieldDoc> {
    
    private boolean prePopulate;

    /**
     * Creates a new instance with <code>size</code> elements. If
     * <code>prePopulate</code> is set to true, the queue will pre-populate itself
     * with sentinel objects and set its {@link #size()} to <code>size</code>. In
     * that case, you should not rely on {@link #size()} to get the number of
     * actual elements that were added to the queue, but keep track yourself.<br>
     * <b>NOTE:</b> in case <code>prePopulate</code> is true, you should pop
     * elements from the queue using the following code example:
     * 
     * <pre>
     * PriorityQueue pq = new HitQueue(10, true); // pre-populate.
     * ScoreDoc top = pq.top();
     * 
     * // Add/Update one element.
     * top.score = 1.0f;
     * top.doc = 0;
     * top = (ScoreDoc) pq.updateTop();
     * int totalHits = 1;
     * 
     * // Now pop only the elements that were *truly* inserted.
     * // First, pop all the sentinel elements (there are pq.size() - totalHits).
     * for (int i = pq.size() - totalHits; i &gt; 0; i--) pq.pop();
     * 
     * // Now pop the truly added elements.
     * ScoreDoc[] results = new ScoreDoc[totalHits];
     * for (int i = totalHits - 1; i &gt;= 0; i--) {
     *   results[i] = (ScoreDoc) pq.pop();
     * }
     * </pre>
     * 
     * <p><b>NOTE</b>: This class pre-allocate a full array of
     * length <code>size</code>.
     * 
     * @param size
     *          the requested size of this queue.
     * @param prePopulate
     *          specifies whether to pre-populate the queue with sentinel values.
     * @see #getSentinelObject()
     */
    CHitQueue(int size, boolean prePopulate) {
      this.prePopulate = prePopulate;
      initialize(size);
    }

    // Returns null if prePopulate is false.
    @Override
    protected CFieldDoc getSentinelObject() {
      // Always set the doc Id to MAX_VALUE so that it won't be favored by
      // lessThan. This generally should not happen since if score is not NEG_INF,
      // TopScoreDocCollector will always add the object to the queue.
      return !prePopulate ? null : new CFieldDoc(Integer.MAX_VALUE, Float.NEGATIVE_INFINITY);
    }
    
    @Override
    protected final boolean lessThan(CFieldDoc hitA, CFieldDoc hitB) {
      if (hitA.score == hitB.score)
        return hitA.doc > hitB.doc; 
      else
        return hitA.score < hitB.score;
    }

}
